1. Technical Field of the Invention
The present invention relates to novel double-stranded RNA oligonucleotides for decreasing tyrosinase expression, to the use thereof for cosmetic and/or pharmaceutical purposes and also to the association thereof with cationic particles less than or equal to 1 μm in size, with a zeta potential ranging from 10 to 80 mV.
2. Description of Background and/or Related and/or Prior Art
Tyrosinase (monophenol dihydroxyl phenylalanine: oxygen oxidoreductase EC 1.14.18.1) is the essential enzyme involved in the mechanism of skin pigmentation. It catalyzes in particular the reaction for conversion of tyrosine to Dopa (dihydroxyphenylalanine) by virtue of its hydroxylase activity and the reaction for conversion of Dopa to dopaquinone by virtue of its oxidase activity. The tyrosinase acts only when it is in the maturation state under the action of certain biological factors.
This enzyme can also be advantageous in the treatment of pathologies such as melanoma (Riley et al., J. Immunother., 2001, 21, 212-220) or Vogt-Koyanagi-Harada disease (Read et al., Curr. Opin. Ophthalmol., 2000, 11, 437-442).
The mechanism of formation of skin pigmentation, i.e., the formation of melanin, is particularly complex and involves schematically the following main steps:                Tyrosine Dopa→Dopaquinone→Dopachrorne→Melanin        
Thus, the pigmentation of human skin results from the synthesis of melanin by dendritic cells, melanocytes. The latter contain organelles called melanosomes, which are the site of melanin biosynthesis. It is the melanosomes which, after migration along the dendrites, are transferred from the melanocytes to the keratinocytes. The keratinocytes are then transported to the surface of the skin during the epidermal differentiation process (Gilchrest B A, Park H Y, Eller M S, Yaar M, Mechanisms of ultraviolet light-induced pigmentation, Photochem Photobiol., 1996; 63: 1-10; Hearing V J, Tsukamodo K, Enzymatic control of pigmentation in mammals, FASEB J., 1991; 5: 2902-2909).
Among melanogenesis enzymes, tyrosinase is a key enzyme which catalyses the first two steps of melanin synthesis. Homozygous mutations for tyrosinase cause oculocutaneous albinism type I characterized by a complete absence of melanin synthesis (Toyofuku K, Wada I, Spritz R A, Hearing V J, The molecular basis of oculocutaneous albinism type 1 (OCA1): sorting failure and degradation of mutant tyrosinases results in a lack of pigmentation, Biochem J., 2001; 355: 259-269).
Since hyperpigmentation disorders result from an increase in melanin production, the development of novel therapeutic approaches, the rationale of which is based on the inhibition of tyrosinase activity, is found to be important.
Most of the skin-lightening compounds already known are phenols/catechols. These compounds inhibit tyrosinase but most of these compounds are cytotoxic with respect to melanocytes, which could cause permanent depigmentation of the skin.
It therefore appears to be advantageous, for an application in humans, to have novel tyrosinase-inhibiting compounds that are both highly effective and exhibit good tolerance.
Of late, the use of double-stranded RNA, dsRNA, oligonucleotides, and more particularly of siRNA oligonucleotides (of 12 to 40 nucleotides), would make it possible to obtain a specific activity in the cosmetic field, such as skin care or hair care, but also in the dermatological and pharmaceutical fields.
However, the use of siRNAs in vivo is known to present various difficulties.
Besides the problem of the penetration of these siRNAs in order to reach the target cells when they are applied topically, due in particular to the difficulty in crossing the stratum corneum, experience has shown that the administration of siRNAs could bring about the triggering of an interferon response reported by numerous publications (Sledz C A et al., Activation of the interferon system by short-interfering RNA., Nat Cell Biol., 2003; 9:834-9. Katalin Karikó et al., Small Interfering RNAs Mediate Sequence-Independent Gene Suppression and Induce Immune Activation by Signaling through Toll-Like Receptor 31, J. Immunol., 2004; 172: 6545-6549. Judge A D et al., Sequence-dependent stimulation of the mammalian innate immune response by synthetic siRNA, Nat. Biotechnol., 2005; 23:457-62) and also the induction or the inhibition of the expression of genes not targeted by the siRNA (Jackson et al., Expression profiling reveals off-target gene regulation by RNAi, Nat. Biotechnol., 2003; 21:635-7), these two phenomena are highly undesirable.
Published U.S. Application No. 2004/0215006 describes double-stranded and anti-sense single-stranded RNA oligonucleotides which are active against tyrosinase; the examples relate only to anti-sense single-stranded RNA oligonucleotides. In particular, it is not demonstrated whether the siRNAs homologous to these anti-sense RNAs are effective.
Some authors have emphasized that double-stranded RNA oligonucleotides, such as siRNAs, and anti-sense single-stranded RNA oligonucleotides have different targets and that the activity of an anti-sense RNA cannot be extrapolated to the siRNA of the same sequence (Xu et al., Effective small interfering RNAs and phosphorothioate anti-sense DNAs have different preferences for target sites in the luciferase mRNAs, BBRC 2003; 306:712-717).
Moreover, in said 2004/0215006, the concentrations of siRNA proposed are from 50 and 200 nM. As indicated above, Jackson et al., have described a strong positive and negative regulation of genes not targeted by the siRNAs used at concentrations of 100 nM.
Similarly, in WO 2005/060536, which describes siRNAs that specifically inhibit tyrosinase, the concentration ranges proposed are very wide and can result in compositions comprising a very large amount of siRNAs for which a positive and negative regulation of genes not targeted by the siRNAs may be observed.
In the context of a cosmetic or therapeutic use, this regulation of non-targeted genes is not acceptable, in particular due to its unpredictable nature.